1. Field of the Invention
This invention relates to a flash light amount controlling apparatus which controls to an appropriate level, the amount of light emitted by an electronic flash toward the main object to be photographed.
2. Description of the Prior Art
Conventionally, cameras having an automatic focus detection (hereinafter referred to as autofocus, or AF) function, and further having the ability to perform automatic exposure while automatically controlling the amount of light emitted from the electronic flash, have been provided. FIG. 25 shows a basic outline of the construction of the optical system of a single lens reflex camera comprising one example of this type of camera. In this camera, when focus detection is performed, the beam of light of the object to be photographed that passes through photo-taking lens 2 is, after it passes through a transparent member of main mirror 12, reflected toward the bottom of camera body B by sub-mirror 14, whereupon it is led to focus detection module 18. On the other hand, when exposure is performed via shutter release operation, main mirror 12 and sub-mirror 14 are pushed together toward the top of camera body B, and the beam of light that passes through photo-taking lens 2 forms an image on film surface F0. At this point, the light reflected from the film surface is led to element 36 of the flash light amount controlling apparatus as the beam of light used for the control of the flash light amount.
The principle of performing focus detection based on the beam of light reflected toward the bottom of camera body B is the TTL phase differential method. FIG. 26 is a type view of an optical system for performing focus detection using the phase differential method. Condenser lens 4 is located in the vicinity of intended image forming plane FS of photo-taking lens 2. This intended image forming plane FS is located in a position equivalent to film surface F0 (FIG. 25). A pair of re-imaging lenses 6 and 8 are located symmetrically with respect to optical axis AX of photo-taking lens 2 at the rear portion of intended image forming plane FS. The image formed on intended image forming plane FS via photo-taking lens 2 is re-formed by this pair of re-imaging lenses 6 and 8. A0, B0 and C0 indicate front-focus, in-focus and rear-focus images, respectively, formed by photo-taking lens 2. Image re-formation lenses 6 and 8 form first and second images A1 and A2, B1 and B2 and C1 and C2, corresponding to front-focus image A0, in-focus image B0 and rear-focus image C0, respectively.
Where front-focus image A0, in-focus image B0 and rear-focus image C0 are formed as images indicated by upward-pointing arrows, the first and second images corresponding to them are formed as images indicated by downward-pointing arrows, and the space between the first image and second image varies in accordance with the focus adjustment status of photo-taking lens 2. Therefore, if, with regard to re-imaging lenses 6 and 8, photoreceptor element arrays are located either at a conjugate position with respect to intended image forming plane FS or in the vicinity thereof, and if the positions of the first image and second image are determined from the output of these photoreceptor element arrays, the focus adjustment status of photo-taking lens 2 may be detected. Incidentally, aperture masks 10-1 and 10-2 are located in front of re-imaging lenses 6 and 8. In this way, the defocus amount may be detected via the space between the first image and second image based on the output from the photoreceptor element arrays.
Incidentally, in FIG. 25, L is an exchangeable lens, 12a is a transparent member of main mirror 12, 10 is an aperture mask, 16 is a mirror box, 16a is an aperture that conveys light to the AF module, 18a is a basket body that fixes and holds all parts of the AF module, 20 is a photoreceptor element package, 22 is a viewfinder mask, 24 is an optical path refracting mirror, 26 is an infrared cut filter, 28 is a Fresnel lens, 35 is a condenser lens, 30 is a pentagonal roof prism, 32 is an eyepiece, 33 is an optical path refracting lens, and 34 is a light measurement element.
FIG. 27 is a type view of the case in which the lengths of all optical paths in the optical system in FIG. 26 are extended. Where the optical path lengths are extended, front-focus image A0 and rear-focus image C0 are re-formed by re-imaging lenses 6 and 8 under the same conditions of the photo-taking lens, and images A1 and A2 and B1 and B2 are formed. When this happens, the distances between images A1 and A2, B1 and B2 and C1 and C2 on the photoreceptor element are wider than in FIG. 26. In other words, the discrepancy in the positions of the re-formed images on the photoreceptor surface vis-a-vis the discrepancy in the same defocus amount becomes larger. Therefore, a small defocus amount discrepancy may be detected by the photoreceptor element, and the accuracy of focus detection may be increased.
However, in the construction shown in FIG. 25, the optical path length of focus detection module 18 is limited by the part housing flash light amount controlling element 36, which limits the accuracy of focus detection. Therefore, there are models in which either the AF photo-electric conversion element or the light amount monitoring element may serve as the flash light amount controlling element, which improves space efficiency, lowers the cost, and improves autofocus performance, but limits the control area for autofocusing and for flash light adjustment. In other words, where the main object to be photographed is within the control area, if flash light adjustment is performed using the element for that area, flash light adjustment appropriate for the main object to be photographed may be performed, but where the main object to be photographed leaves the control area, for example during panning, control of the flash light amount can no longer be performed properly.
Incidentally, it is known that in order to obtain a proper exposure of the main object to be photographed with a camera having an autofocus function, the photo-taking screen is divided into multiple areas, for each of which light measurement and focus detection are performed, and flash light adjustment is carried out, with an emphasis on the area containing the main object to be photographed, based on the measurement information obtained from the multiple areas.
In addition, in a camera with various AF modes (continuous AF, AF lock), because the focus detection information becomes inaccurate if camera shake occurs, a method to change the AF mode to an appropriate setting based on a determination that the camera is shaking is known (for example, see Japanese Patent Laid-Open Application No. 3-161722).
Furthermore, in a camera in which AF lock is performed at the time of focusing, and in which the exposure amount setting to control exposure is simultaneously locked (AE lock), the AE lock is released in order to obtain an appropriate exposure, even where the object to be photographed is a moving object (e.g., Japanese Patent Laid-Open Application No. 1-288818).
However, in none of the above devices is it concretely shown how control of flash light adjustment is performed when the object to be photographed leaves the autofocusing and flash light adjustment control areas.
In addition, in U.S. Pat. No. 4,429,966, in a contrast detection type AF camera, a single member serves as an AF sensor and as a photoreceptor element for flash light adjustment, and light adjustment of the flash light is performed using an AF sensor array.
Moreover, in U.S. Pat. No. 4,791,446, fixed light measurement is performed using an AF sensor integral time control monitoring element, but this monitoring element is not used to perform flash light adjustment. The AF sensor and the monitoring element are on the same chip, and there is no photoreceptor element located elsewhere other than on this chip.
Furthermore, in U.S. Pat. No. 4,974,005, both AF lock and AE lock are provided; when AF lock is on, AE lock is activated as well, and if it is subsequently determined that the object to be photographed is a moving object, AE lock is released. However, there is no disclosure regarding flash light adjustment.
In addition, in U.S. Pat. No. 4,494,850, control of the flash light amount alternates between flashmatic (FM) and flash light adjustment in accordance with the focal length of the photo-taking lens. However, it does not alternate between FM and flash light adjustment in accordance with the AF mode. Moreover, where the object distance is unreliable, it alternates between FM and flash light adjustment.
Furthermore, the camera in U.S. Pat. No. 5,231,447 changes the priority of multiple flash light adjustment areas depending on whether the AF mode is continuous AF or single AF. However, switching of the flash light amount control method does not occur in accordance with the AF mode. Moreover, there is no disclosure that the flash light adjustment area changes when panning is occurring.